(1) Field of the invention
This invention relates to a method of and apparatus for strapping a plurality of individual tiles together to form a package. More particularly, the invention is concerned with the packaging of extruded concrete roofing tiles.
In extrusion processes for manufacturing concrete roofing tiles, the tiles are continuously extruded on pallets and are fed on a conveyor system incorporating belt conveyors from the tile extrusion machine to a depalleting device, usually via a curing zone in which the tiles are partially cured. After depalleting, the tiles are removed from the conveyor and stacked in the open air for curing or to complete the curing process as the case may be.
In order to avoid manual handling of large numbers of uncured or partially cured individual tiles, involving at least one operative with the attendant possibility of the tiles being damaged during removal from the conveyor line, stacking in the open air and transport to site, various systems have been devised for arranging the tiles in successive stacks comprising, for example 40 tiles, and securing a strap or band around each stack of tiles to form a package. By this means the number of individual units which have to be dealt with is considerably reduced, the tile packages can be handled by machines and the risk of breakage is largely eliminated.
In strapping stacks of concrete roofing tiles it is desirable, if not essential, that the strap be secured around the ends of tiles in the central longitudinal region of the stack in order to avoid damage and possible breakage to the interlocks extending along opposite sides of the tiles, during tensioning and securing of the strap. Power strapping machines are known for strapping cartons and have also been used for packaging tiles. One such strapping machine comprises a rectangular chute frame formed of inwardly opening channel sections in which a strap of plastics material is fed from a reel, the carton being fed into the space within the frame under the control of an operator so that the strap encircles the carton. The machine is then operated whereby the machine wraps the strap around the carton, tensions and secures the strap as by heat or friction welding, crimping or clipping.
(2) Description of the prior art
Such a power strapping machine is used in one packaging system known to the Applicants for strapping clay roofing tiles formed on a belt conveyor into a horizontal stack in which the tiles are disposed upright one behind the other on one of their edges and are held by hydraulic clamping devices in the stack to maintain the tiles upright. Since, a strapping machine having a rectangular chute frame cannot be used to strap the horizontal stack of tiles whilst on the belt conveyor, the stack is removed by means of the clamping devices to a roller conveyor adjacent the belt conveyor where the chute frame is positioned between adjacent rollers and the stack whilst remaining clamped is fed into the chute frame for strapping.
Also known to the Applicants is a system for packaging extruded concrete roofing tiles which involves the forming of a horizontal stack of tiles on a belt conveyor and clamping of the stack to maintain the tiles in an upright position. In this system, the conveyor is stopped at a strapping location where an open bottomed chute frame mounted on a moving trolley is positioned over the clamped stack of tiles. Then a bayonet carrying one end of the strap extending around the chute frame is fed through a channel disposed between two runs of the belt conveyor and the strap is then wrapped around the stack. Stopping of the conveyor for the strapping operation is disadvantageous since the stacking and strapping operation has to be synchronized precisely to the speed of the extrusion machine which may operate at speeds upwards of 4000 tiles per hour. Moreover, bayonet feed of the strap can give rise to problems.
Two other known systems involve the use of turntables on which extruded concrete roofing tiles fed from a belt conveyor system are stacked flat one on top of the other. The turntable is then turned to bring the vertical stack of tiles to a station at which is located a stationary strapping machine. Since the tiles are stacked on the turntable, the chute frame of the strapping machine has to be at least partially open at the bottom and the strap must be fed by hand across the opening before the machine can wrap the strap around the tile stack. In these systems, the stack is supported on a slotted base on the turntable so that the strap can be wrapped around the stack. After strapping, the turntable is turned to another station where the tile package is clamped, rotated into a horizontal position and placed on another conveyor system.
All the above systems involve the use of complicated and expensive apparatus, and sophisticated electrical control systems for synchronizing the stacking and strapping operations to the speed of the conveyor systems used and in the cases of extruded concrete roofing tiles to the speed of the extrusion machine. In the systems using turntables, stacking of partially cured or uncured tiles flat one on top of the other leads more easily to tile damage. Moreover, the apparatus have large numbers of moving parts which can be expensive to maintain and which can more easily breakdown in the dusty environment of a tile making factory.
Accordingly, it is an object of the present invention to minimize or overcome the aforementioned disadvantages by providing a system for packaging tiles in which the apparatus has fewer moving parts, is simpler and less expensive than the aforementioned apparatus, which can strap stacks of tiles on a belt, band or chain conveyor without stopping the conveyor and which can utilize a strapping machine having a rectangular chute frame.